DESCRIPTION (provided by investigator): We have discovered mutations in the senataxin gene (SETX) as the molecular basis of a juvenile-onset, autosomal dominant (AD) form of familial amyotrophic lateral sclerosis (ALS). This form of ALS, known as ALS4, is an essentially pure motor systems disorder characterized by limb weakness, severe muscle wasting, pyramidal signs, and slow relentless disease progression. Senataxin is a large 2677 amino acid protein which contains a conserved superfamily 1, DNA/RNA helicase (of ~ 500 amino acids) in the C-terminus, strongly suggesting a functional role in RNA processing. While the precise function of senataxin remains unknown, the most compelling evidence including more than 10 years of functional studies of the yeast ortholog sen1p suggest these proteins function in several RNA processing events including RNA Pol II transcription termination of short <500-nt transcripts. As it turns out, altered RNA processing in neurodegeneration is well established including loss of SMN in spinal muscular atrophy (SMA) and loss of FMRP in fragile-X mental retardation. However, the recent discovery of the involvement of TDP-43 and FUS in familial and sporadic ALS (FALS and SALS) reemphasizes the role of altered RNA processing in ALS. To further study the role of SETX mutations in ALS4 we have created a number of important reagents including transgenic (Tg) and gene targeted mice. We will also isolate neuronal RNA directly from tissue to characterize RNA processing pathways that are aberrant in ALS4 and other FALS/SALS forms. To further our understanding of this form of FALS we recently established Tg mice expressing R2136H mutant senataxin at high levels from the mouse prion promoter (PrP). These R2136H Tg-mice display a motor deficit by rotarod and strength testing beginning at 6-8 months of age. In addition, we have generated Setx gene-targeted mice by introducing a second ALS4-associated mutation, L389S. The L389S KI-mice show a more severe but later onset hind-limb paralysis (~ 12-13 months age) with apparent reduced survival rates. Therefore, we propose to thoroughly characterize these SETX murine models via molecular genetic analysis, behavioral testing, histopathology, immunofluorescent and electron microscopy. Next, we aim to define the subset of neuron expressed RNA transcripts (coding or non-coding) misregulated in response to ALS4 associated SETX mutation. Transcripts identified as most affected by SETX mutation will be validated by quantitative RT-PCR and the role of SETX in transcription termination in specific transcript classes will be tested. In additional experiments we will test if the different RNA processing pathways found to be affected in ALS4 might also be affected in other forms of motor neuron disease. PUBLIC HEALTH RELEVANCE: Narrative Mutations in senataxin (a DNA/RNA helicase) are known to cause of two severe, debilitating neurodegenerative conditions, ALS4 and AOA2. This underscores the importance of senataxin function in the survival of various neuronal populations. Our studies seek to determine the molecular mechanisms leading to motor neuron loss in ALS4 and further characterize the